(1) Summary of the Invention
The present invention relates to a bacterial method and compositions for inhibiting mold and psychrotrophic bacteria in creamed Cottage cheese. In particular the present invention relates to a method which uses mixed bacterial concentrates of Streptococcus lactis subspecies diacetylactis and Propionibacterium shermanii to provide the inhibition of spoilage microorganisms in creamed Cottage cheese.
(2) Prior Art
Extended shelf life of creamed Cottage cheese is of considerable commercial interest. The primary cause of spoilage is gram negative psychrotrophic bacteria, primarily pseudomonads. Mold is a secondary, but also important, cause of spoilage. Control of these spoilage organisms is readily accomplished by incorporating a chemical preservative in the creamed Cottage cheese.
The preservative can be added by direct addition of the active chemical. For example, potassium sorbate at levels between 0.05% and 0.07% in Cottage cheese effectively inhibits psychrotrophic bacteria and mold. The added sorbate must be declared on the ingredient statement and this is thought by some consumers to detract from the natural concept of Cottage cheese.
Another approach to direct addition of a preservative is to add a naturally derived non-viable antimicrobial product to the Cottage cheese. This product can be declared as a natural ingredient on the label. A commercial product of this type is a milk based mixture of naturally derived organic acids (including acetic and propionic acids). This product claims to be effective against psychrotrophs and mold and can be declared as milk on the ingredient statement of the container for the Cottage cheese. The rather dilute product (7% solids) must be used at a 1% by volume rate in creamed Cottage cheese and must be stored at refrigerator or freezer temperatures which is disadvantageous.
The prior art has described the use of Streptococcus lactis subspecies diacetylactis in Cottage cheese cream dressing to inhibit psychrotrophic bacteria but not mold. This use is described in U.S. Pat. Nos. 4,172,899 and 4,191,782 to Vedamuthu, 3,968,256to Sing and 4,477,471 to Gonzalez. In these methods the Streptococcus lactis subspecies diacetylactis is added to the Cottage cheese cream dressing under refrigeration conditions and the Streptococcus lactis subspecies diacetylactis produces an inhibitory substance which inhibits psychrotrophic bacteria and develops a diacetyl flavor in the Cottage cheese cream dressing if the citrate metabolizing characteristic has not been altered in the strain used. The problem is that mold is not inhibited in the Cottage cheese cream dressing by the inhibitory substance from Streptococcus lactis subspecies diacetylactis.
Streptococcus lactis subspecies diacetylactis has been used with the non-viable fermented milk product and the combination produces effective results. The disadvantage of this method is that the use of the fermented milk product is still required.
Each of the available prior methods for control of spoilage organisms in Cottage cheese has its disadvantages, either real (high cost, limited spectrum) or perceived (preservative added versus all natural). A culture system was needed that combined the natural concept and cost effectiveness of a culture with the broader spectrum available by direct addition of preformed antimicrobials.
It had been thought by those skilled in the art that Propionibacterium shermanii had to be fermented in milk and then the bacteria killed, such as by heating, to produce the non-viable fermented milk product with the mold inhibiting substance. It had not been believed that the inhibitory substances generated by this bacterium would develop in the Cottage cheese cream dressing with Streptococcus lactis subspecies diacetylactis, particularly since it was thought that insufficient organic acids would be produced at the low incubation temperatures encountered in refrigeration.